1. Field of the Invention
The present invention relates to a magnetic recording disk (known as a hard disk) where a magnetic layer is formed on a circular rigid substrate.
2. Description of the Prior Art
It is generally customary that circular magnetic recording disks adapted for random access are widely used as storage media in computers and so forth. Out of such-storage media, particularly a hard disk with a substrate of aluminum alloy or the like is employed as a stationary or external disk due to a high response speed and a great storage capacity.
In such magnetic recording disk (hard disk), with respect to the running facility and durability thereof, an adequate surface roughness is required with extremely fine irregularities on its surface which is to be in contact with a magnetic head. For example, there is known a texturing process which is a technique of lapping the surface of a circular rigid substrate in the circumferential direction and forming extremely fine scars to thereby control the surface roughness.
In this case, the surface roughness of the magnetic recording disk is restricted principally by the flying distance of the magnetic recording head and the CSS (contact start-stop) characteristics. And any excessive surface roughness causes a trouble termed head hit, while any insufficient surface roughness causes an increase of the friction coefficient to the magnetic recording head.
It is therefore examined of late to enhance the durability and eliminate undesired adhesion of the magnetic recording head by first evaluating the surface roughness of the magnetic recording disk on the basis of the average roughness Ra at the center line and then optimizing such roughness to reduce the maximum frictional force against the magnetic recording head (as disclosed in Japanese Patent Laid-open No. Sho 62 (1987)-46429).
From the studies promoted by the present inventors with respect to the CSS durability which is the most important characteristic in the magnetic recording head, it has been concluded that a satisfactory result is not attainable merely by prescribing the average roughness at the center line.